The meaning of Fermentation
In a broad sense an (ordinary meaning)It is a reaction of organic matter being resolved by a microbe.
Only the good things for humans are called "Fermentation" and the bad things are called "decay".
In a narrow sense (a techunical meaning)Fermentation is a reaction in which carbhydrates are broken down into microbe without oxggen.
NADH make from oxidized substrate are oxidized and reproduced as NAD＋